


Anatomy Lesson

by his_valentine



Series: Sheith Vignettes [8]
Category: Voltron: Legendary Defender
Genre: Alien Sex, Anal Sex, Bottom Shiro (Voltron), Established Relationship, Galra Keith (Voltron), M/M, Plot What Plot/Porn Without Plot
Language: English
Status: Completed
Published: 2018-05-16
Updated: 2018-05-16
Packaged: 2019-05-07 18:07:53
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,371
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14676561
Author URL: https://archiveofourown.org/users/his_valentine/pseuds/his_valentine
Summary: Shiro wanted to see how far down the cheek mark went (he gets to find out a lot more.)





	Anatomy Lesson

Once they were alone, Shiro paused in the hallways. Noticing the lack of following footsteps immediately, Keith also stopped and turned to him. He tilted his head curiously, and Shiro brushed his fingers along Keith's cheek, the one with the new mark.

When Keith didn't shy away, just kept giving him that same guarded stare, Shiro pressed onward, cupping his hand around Keith's jaw and brushing his thumb over the actual mark.

From afar, it had looked like a discolored patch of skin, or maybe a very clean-lined bruise. Shiro discovered that the purple coloration was actually a faint covering of hair. It was short and thick, almost like facial hair, but soft instead of wiry. More like silky fur than anything else.

"I know, it's weird," Keith said cautiously as Shiro smoothed his thumb over it once more, in the other direction so that it ruffled and stood out more obviously.

"Weird, yeah. I don't mind, though." Shiro said absently, before looking away from the mark and at Keith's actual face. "Did you always have this?"

"No," Keith said first, but then thought about it and ammended, "Kinda? I guess... Galrans and Alteans are distantly related, so Galrans can do minor shape-shifting. I was subconsciously choosing to look more human because that's what I've always been surrounded by. Since I've been with the Blade, I've been... changing," he backed away just a bit, out of Shiro's reach.

Shiro nodded, crossing his arms over his chest. "It doesn't hurt, does it?" he asked.

"It itches more than anything," Keith said with a shrug. Shiro smiled in relief and stepped back into his space. He then glanced up and down the hall for any witnesses before crowding Keith even closer.

"How far does it go down?" Shiro asked, quietly. Keith blushed and made to step back again, only to bump his heel against a pillar. Which meant Shiro was probably doing this on purpose.

Which normally, would have been fine. Great, even. But Keith felt himself growing cold, not warm, as he realized sooner or later he'd have to tell, and maybe even show, his boyfriend the changes that had occurred underneath his clothing. Sooner, if the look Shiro was giving him was any indication. "I, uh," Keith mumbled, at a loss.

Shiro lost the smoldering look and gave out a good natured chuckle, stepping away. "Too quick? I understand if you're not-"

"Tonight," Keith punched out, deciding to just get it over with. Well, later anyway.

"Hm?" Shiro hummed, blinking.

"Come to my room at 22-hundred. I'll show you then," Keith promised, to both his boyfriend and to himself, before he suddenly sidestepped past Shiro and took off.

Shiro watched him go, slightly worried. Whatever had Keith worked up like that, regarding his changes... He had an inkling, since it seemed his flirty little question had triggered the shift in mood.

* * *

Keith sat on the edge of his bed, leg bouncing out of nervousness. He was dressed only in his briefs, figuring that he'd get the majority of it out of the way as soon as Shiro walked in. The top hem of his underwear was folded down at the back and rumpled in front, since he hadn't altered his old clothing yet.

The fuzzy little tail he'd sprouted thumped against the bed on every other leg bounce, impatient, as he watched the clock. At the moment it rolled over from 2159 to 2200, there was a knock at the door. Keith smiled wryly, knowing that meant Shiro had probably been hovering around his door for the past 30 seconds or so. He always was punctual. "Come on in," Keith called out.

The door slid open and luckily, it was Shiro. The older man stepped in, door closing behind him. "Kei-" the words died on his tongue as he stared at Keith, eyes widening. Keith ducked his head down, looking equal parts embarrassed and nervous.

The mark on his cheek didn't go down much further than his collarbone, but there was a series of stripes wrapped around his sides, with two heavier ones that wrapped up around his shoulders. The fur was thicker there, especially where all the stripes met along his spine and followed down the middle of his back to his tail.

Said tail curled forward, draping protectively across his own lap as he waited for Shiro to do something other than stare at him.

"Is that a tail?" Shiro asked. He stepped closer, and he didn't sound disgusted, so Keith glanced up at him. When he saw the curious look of wonder on Shiro's face, his tail subconsciously thwapped against his thigh, feeling less self-conscious already.

Shiro came over and sat next to him, just now seeing the fur going down his spine. "Are you going to grow fur everywhere?" he asked softly as he reached over to brush his fingers through it.

Keith let out a little noise, back arching. "I... I don't know," he stammered.

"Is this alright?" Shiro asked softly as he started to dig his fingers through the thick purple fur. Keith shivered and leaned back, nodding. He wasn't sure that his voice wouldn't crack.

Shiro hummed and turned to him, folding one leg up onto the bed, then leaned in and kissed the fur on Keith's shoulder. "I could get used to this," he murmured into the fluff.

Keith blushed, smiling softly. "Well, I'm glad you think that..." he paused, looked down at his lap, then sighed and added on, "so far, anyway."

"So far?" Shiro asked, putting his hand on Keith's thigh. He blinked when he realized that the rest of Keith's old body hair had also softened and thickened. "Is there... more?" he questioned expectantly.

"I, uh," Keith stammered, lost his words, and decided to speak in actions. He reached down and wiggled out of his briefs, nervousness twisting his stomach as he kicked them off. Even with his anxiety, if not in spite of it, he took hold of his polymorphed dick and looked over to see Shiro's reaction.

"That's... different," Shiro said, staring in shock. "It, uhm, looks like it still works the same way, though. Is this what you were worried about?"

"I mean, yeah? It looks..." Keith glared at it dourly, "gross, and that's before it even gets hard," he bit his lip as it started to twitch, the tapered glans flaring noticably.

"I didn't say gross, I said different," Shiro soothed, leaning against him suddenly, voice low and quiet. He reached down between Keith's legs and wrapped his hand over top of his. "If I have to be completely honest for you to believe me, I think it looks... interesting," he pressed his face into Keith's hair, mildly embarrassed by the confession already.

"Heh," Keith breathed softly, "interesting? How do you mean?" he asked flirtatiously, his own hand dropping away so that Shiro's could take over on the teasing, slow strokes.

"I..." Shiro started, then paused, "I want you to fuck me tonight," he mumbled, quickly and quietly. Keith bit out a moan at that, his cock thickening enough now for the ribbed ridges to form along the underside. "God, Keith. You got bigger, too," Shiro moaned, peeking over his hair to take another long look at it.

Keith leaned into Shiro as he started to stroke more firmly. The barest brush against the underside of the flared glans would make him whine or yelp, startling as if it was a bit too much, but focusing on the ridges further down made his cries pitch lower and his hips roll.

Once Keith was sufficiently worked up, cock standing proud and throbbing, Shiro leaned away briefly to fish the lube out from under the pillow. He glanced over at his boyfriend again, who was watching him closely. Shiro shuffled back until he was leaning on the wall with mostly his shoulders, lower back flat against the bed, then popped open the lube and dolloped it heavy on his fingers.

As embarrassed as he was, he knew Keith would appreciate it as he spread his legs wider and reached around from underneath himself to keep the view unblocked, forcing his back to arch out as he slid in the first finger. He heard the heavy groan that the younger boy let out as he shuffled closer.

They locked eyes for a moment, Shiro's expression open and eager as Keith's darkened possessively. "More," Keith nearly growled, and Shiro jumped to obey, breath hitching and head lolling when the second finger slipped in.

"Takashi, you're so fucking hot," Keith praised, crawling even closer so that he was kneeling in between Shiro's thighs, holding onto the older man's knees as he watched, chest heaving and flushed. By now his cock hung heavy between his legs, a distinct purple shade from both the recessive Galran genes and arousal. "Come on, open yourself up for me," he groaned, as his hips jutted forward impatiently.

Shiro felt just as impatient, especially as Keith's cock brushed against his and he realized with a soft little whimper that at this point, Keith was the bigger out of the two. Keith seemed to realize this as well, watching their cocks slide together with rapt wonderment.

Shiro closed his eyes and started to roll his hips, letting out soft little gasps as he was grinding either up against Keith's thick, imposing alien cock, or down onto his own scissoring fingers.

Before long, he was plunging three fingers in and out of himself roughly. He tried to pull Keith closer as his hips started to falter, but Keith huffed and pulled back instead. "Baby?" Shiro asked, sounding desperate and needy for it.

Keith had to close his eyes, growl, and squeeze the base of his cock just to keep from blowing his load all over the sight Shiro made. "Come on, aren't you ready yet?" he asked, sounding almost frustrated about it.

"Yeah, alright," Shiro panted, withdrawing from his hole and unarching his back before he rolled over and presented himself, burying his face into a pillow preemptively. Keith let out another deep, shuddery sigh.

There was some shuffling, and the distinct squirting noise of Keith using up the last of the lube - Shiro did make a note to grab more from the medical bay before Keith's slender fingers, three at once, slipped into him. "Mm, yeah, you'll be loose enough," Keith said, wiggled his fingers, then pulled free. Shiro just moaned softly in response, though his hole clenched.

The tip slid in, easier now that it was more tapered, and the glans popped in afterward. Keith inhaled sharply and pushed in further, up past the first ridge, before he paused, his hands tightly gripping at Shiro's waist. "F-fuck," he groaned, looking down at where they were connected, "Takashi? Uh... are you okay?" he asked, sounding nervous.

Shiro turned his head to glance back at Keith, face flushed and expression heavy. He did seem a little concerned about the worry in Keith's voice, but as for himself... He held up a thumb, signaling that he was great.

"It's just, with how the tip is now, it kinda feels weird to pull back... I think I'm supposed to rut," he explained, voice hitching as he sank down deeper and started to show Shiro what he meant. He pinned Shiro as best he could with the entirety of his body weight, bouncing his hips off Shiro's ass like he was only trying to get deeper.

Shiro's breath hitched, eyes fluttering as the ribbing on the underside was forced to rub against his prostate by the sheer girth of Keith's new, magnificent cock. When he lifted his hips, Keith's hands slid in underneath, pulling at them and helping Shiro back up onto it. Keith curled over his older boyfriend from behind, forehead braced against the wide expanse of Shiro's upper back.

Shiro lifted his head from the pillow for a deeper breath, but he looked absolutely wrecked. When Keith's grinding started to pick up in speed, Shiro started to whine softly, giving into his subspace. Keith seemed to pick up on the change in tension beneath him, because he growled out a triumphant, "Fuck yeah, give in, you're so good for this."

Keith's grinding started to stutter and slow, but he was groaning like he was still only almost there. Suddenly, he stopped completely, hips pressed inward and flush against Shiro's ass, then let out a keen.

Shiro's eyes flew open when he felt that not only the tip, but each ridge inside of him, had flared wider. Keith panted roughly as he ejaculated, at least at first. He'd caught his breath by the time his load started to trail off, though, and looked mostly confused at the feeling by the end.

"Did you...?" Shiro asked. He was pretty sure that's what had happened, but it had been just different enough to make him second guess himself.

"Yeah. I can- ah?" he had tried to slip out, but the flared head was still open, making it uncomfortable to do so. Shiro had inhaled sharply as well, feeling overstuffed and sensitized to the slightest movement.

"Ugh, please baby," he pleaded, trying to grind into the sheets. Keith nuzzled closer to his back and reached around, stroking his cock. Shiro's eyes rolled back and he whimpered brokenly as he let go, cum dripping over the back of Keith's hand.

The clenching of his hole triggered a secondary, less physical release in Keith. He sighed in relief as he felt his cock finally begin to soften, his flare settling back down until he could finally pull free.

Keith flopped over, onto his back next to Shiro. He stared at the ceiling, suddenly realizing how winded and sweaty he'd gotten. "That was amazing," he groaned, voice even rougher than usual.

"Mmhm," Shiro sleepily agreed. He hadn't moved yet, so Keith leaned up and drank in the view. The leader of Voltron, face-down and unable to even form words as cum started to ooze out of his ass. Keith chuckled and laid back down after he'd gotten his fill of eyecandy, realizing that, as usual, Shiro had fallen asleep already.

Whatever, Keith figured, a nap couldn't hurt.

**Author's Note:**

> I feel like im bad at tagging so if u have tag suggestions for this fic (or any of my others) please tell them to me


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